Advanced Crew Served Weapon (ACSW)
Objective Crew Served Weapon (OCSW)

The Advanced Crew Served Weapon was a lightweight and flexible design to defeat variable threats. The low recoil of the 25mm component (XM307) and .50 caliber component (XM312) resulted in lightweight design and stable system for enhanced accuracy and dispersion. Low system weight reduced vehicle mount size and allowed for easy dismount and portability. Full solution fire control provided for first burst lethal fires with 25mm airburst and armor piercing effectiveness to 2000 meters. The modular design of the 2 components allowed quick operator level conversion from 25mm to .50 caliber with 4 parts and no special tools. The XM312 provided mission versatility and a low cost, live fire training device. The Advanced Crew Served Weapons program was an outgrowth of the Objective Crew Served Weapon program.

The Objective Crew Served Weapon (OCSW) program dated back to 1994. The program sought to develop a lightweight, crew portable weapon system, that would use a 25mm family of ammunition (including programmable airbursting ammunition) at a rate of fire of at least 250 rounds per minute. The OSCW would feature a full ballistic solution to make the best use of programmable ammunition, featuring muzzle velocity correction, target acquisition/fire control system laser rangefinder, and target tracking. The program was initially managed by the Joint Service Small Arms Program (JSSAP) Office, US Army Armament Research, Development and Engineering Center, Picatinny Arsenal, New Jersey.

The OCSW, which constituted the weapon subsystem portion of the Land Warrior program, was an integrated machine gun system, which coupled the firepower of airbursting munitions with optoelectronic fire control to provide all-environment operation and enhanced lethality. The OCSW was an ultra-light, 2-man portable, crew-served weapon system incorporating state-of-the-art electronics, advanced materials, and small arms technologies. The unique weapon permited a high probability of incapacitation and suppression of enemy soldiers up to 2000 meters away and had a high potential to damage lightly armored vehicles, water craft, and slow-moving aircraft beyond 1000 meters. The OCSW was the potential replacement weapon for the 40mm Mk 19 Mod 3 grenade machine gun and the .50 caliber M2 machine gun.

The OCSW fired up to 260 25mm rounds per minute in either automatic or semi-automatic mode. The trajectory of the rounds were flatter than those of the Mk 19 Mod 3, which brought more rounds on target faster. The weapon had dual hand grips, which allowed the gun to be raised or lowered and moved laterally with a touch of a button. This meant the gunner never had to take his hands off of the weapon. It used a Direct View Optics similar to the Objective Individual Combat Weapon (OICW). The biggest advantage over the Mk 19 Mod 3 was the weight. A Mk 19 Mod 3 weighed about 140 pounds, while the OCSW weighed 37 pounds with the tripod. Its light weight could increase the number of mission roles the OCSW could handle over the Mk 19 Mod 3. A 2-man team could easily carry it into combat and it took about a minute to set up. The OCSW was in the same development stage as the OICW as of 2000.

The 25mm OCSW was a next generation infantry weapon providing accurate, long range, high explosive, airburst firepower in a compact, self-contained, light weight package. The system consisted of an advanced weapon and mount, a target acquisition/fire control system, and advanced ammunition. The OCSW had high potential for widespread use as a primary or secondary armament for a variety of vehicles and could be quickly dismounted and put into action on the ground. The 25mm system had a full solution fire control system, including a laser range finder and a day/night sight. It delivered highly lethal and suppressive fire out to 2,000 meters against personnel targets, light material targets and vehicles.

The OCSW's original specifications were for a weapon weighing 32 pounds, including its mount, with a full solution, day/night, all weather fire control system. It would be operationally insensitive to enviornmental conditions. The weapon would have up to 18 inches of tripod height when ground mounted and would be 2-man portable. The system would also be capable of being vehicle mountable. The weapon would fire at 260 rounds per minute, in either automatic or semi-Automatic fire modes, and be lethal and suppressive out to 2,000 meters. The shot dispersion would be less than 1.0 mils, one sigma radius. The weapon's 25mm ammunition would include a programmable airbursting round, as well as traditional high explosive and armor piercing types (and complimentary training rounds). The ammunition would be loaded in ammunition cans, capable of being mounted on the weapon, and fed from the left or the right.

In January 2001 the Joint Services Small Arms Program office of the US Army ARDEC/TACOM Command at Picatinny Arsenal, New Jersey awarded Primex Technologies a $17.0 million contract modification for the Advanced Technology Demonstrator Program for the Objective Crew Served Weapon System. This award brought the total contract value to $45.2 million for the OCSW system development program. Three systems and advanced ammunition were scheduled for delivery to the Aberdeen Test Center in June 2002 for technical, safety and early operational assessment testing.

In FY03, the Advanced Crew Served Weapon (ACSW) program successfully transitioned from the Objective Crew Served Weapon Advanced Technology Demonstrator, the predecessor program on which the ACSW was based. ACSW's key capabilities included the successful technology demonstration of the 25mm air bursting munitions, warheads, recoil management, and fire control required to increase the lethality of the weapon over the systems it was targeted to replace, the M2 .50 caliber machine gun and the Mk 19 Mod 3 40mm grenade machine gun. The 25mm ACSW was subsequently designated as the XM307.

On 7 January 2003, General Dynamics demonstrated a .50 caliber variant of the XM307, known internally as the XM307K50. Initially 5 parts were different between the two weapons, and the performance and physical characteristics of the XM307K50 exceed other crew-type .50 caliber weapons. This weapon was subsequently designated as the XM312. The XM312 was intended as a fallback to the XM307, which reduces overall cost to ACSW program. Using existing .50 caliber ammunition increased weapon reliability. It leverages the accuracy and lightweight characteristics of the 25mm weapon to provide a highly accurate lightweight .50 caliber weapon.

General Dynamics Armament and Technical Products was the lead developer and systems integrator for the XM307 25mm ACSW system. Design and development of the weapon would occur at General Dynamics' Burlington, Vermont facility. General Dynamics Ordnance and Tactical Systems of St. Petersburg, Florida was developing the family of 25mm ammunition. Raytheon had responsibility for the design and development of the full-solution fire control.

As of early 2004, the Advanced Crew Served Weapon had met all Advanced Technology Demonstration exit criteria, and had entered the System Development and Demonstration (SDD) phase.

In 2004, as a result of the Common Close Support Weapon (CCSW) Weapon Trade Study, the ACSW was selected as the foundation for the Future Combat Systems (FCS) CCSW program. It was planned that the XM307/XM312 would be the dismounted infantry crew served weapon and defensive armament system for 7 variants of the Future Combat System.

As of May 2005, the ACSW program was in system design and development with the US Army's Program Executive Office Soldier. PEO Soldier was in the process of developing a remotely operated variant (ROV) for FCS manned and unmanned vehicles as part of the CCSW program. Project Manager Crew Served Weapons stated at that time that there was the potential to accelerate 25mm crew served variant and ammunition for Stryker Brigades and ground force units, as well as type classification as standard of the .50 caliber ACSW variant.

With the termination of the manned components of the FCS program in 2008, the decision was made to effectively shelve the ACSW program. The experience gained in the development of an advanced lightweight .50 caliber machine gun to replace the existing .50 caliber M2 machine gun was spiraled out into the development of what became the XM806 machine gun.